Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Expected Credit Losses on Premiums Receivable - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2024 |
Mar. 31, 2023 |
|
| Credit Loss [Abstract] | ||
| Premiums receivable (net of allowance for expected credit losses), balance, beginning of period | $ 10,282 | $ 8,922 |
| Premiums receivable (net of allowance for expected credit losses), balance, end of period | 10,829 | 9,483 |
| Premiums receivable, allowance for expected credit losses [Roll Forward] | ||
| Premiums receivable, allowance for expected credit losses, beginning balance | 69 | 77 |
| Current period change for expected credit losses | 12 | 10 |
| Write-offs of uncollectible premiums receivable | 13 | 10 |
| Premiums receivable, allowance for expected credit losses, ending balance | $ 68 | $ 77 |